[vsnet-alert 25772] V1405 Cas brightening

[Taichi Kato]

V1405 Cas brightening

   V1405 Cas is brightening now.  Several observers
in Japan reported vis or V=7.4 on Apr. 26.

  YYYYMMDD(UT)   mag  observer
  20210421.726    79  (Hiroyuki Maehara)
  20210421.876    79  (Gary Poyner)
  20210422.233  8.18C  (Gary Poyner)
  20210422.875    79  (Gary Poyner)
  20210424.228  7.97TG  (Gary Poyner)
  20210425.882    77  (Gary Poyner)
  20210427.219  7.51TG  (Gary Poyner)

   The recent change in the spectrum (ATel #14577,
V1405 Cas (= PNV J23244760+6111140) now displaying
Fe II emission) most likely reflected this state
change.  The nova before this brightening was
apparently in "premaximum halt" and the unusual
(He/N) spectroscopic feature for a slow nova
may have been because the nova was still well
before the maximum.

   The change from premaximum halt to maximum
is different from what was observed in V723 Cas
https://ui.adsabs.harvard.edu/abs/1998A%26A...338.1006I/abstract

   Assuming V=8.0 for the premaximum halt and
an extinction of 1.3 mag, M(V) of the premaximum
halt is -4.6.  Using the relation in Hachisu and Kato
(2004 ApJ 612, 57), this value yields an unacceptably
small mass of the white dwarf.  If the extinction
is not severely underestimated, the result suggests
that Hachisu and Kato's assumption that the premaximum
halt reflects the Eddington luminosity would be
invalidated.

   Taguchi-san, do you have any estimate for
the bolometric luminosity during the premaximum
halt?  If the bolometric correction is large,
the discrepancy may be avoided.